1. Field of the Invention
The invention relates generally to the field of digital radio signal communications. More particularly, the invention relates to measuring signals received at different antenna arrays to determine transmit parameters for multiple transmit antenna arrays.
2. Description of the Related Art
Radio communications are sensitive to the environment in which the radio signals are transmitted and received. Communications can be lost or degraded when the environment is not favorable to the type of signals being transmitted. One particular environmental problem is fading due to scattering. This problem can cause multipath interference or completely prevent reception of a transmitted signal. One known way to mitigate fading due to scattering is to use receive or transmit diversity. Spatial receive diversity typically uses two receive antennas spaced a distance from each other. The receiver will either choose the antenna that receives the strongest signal or combine the signals from both antennas.
Delay receive diversity uses a single antenna and searches for multipath copies of a signal delayed in time. A RAKE receiver or an equalizer then combines the two or more signals to resolve the original single signal. Many digital cellular telephones are required to have receivers that can resolve signals with a number of chips or symbols of delay spread depending on the system.
Transmit diversity works much like receive diversity in reverse. Signals can be transmitted from spaced apart antennas. Transmit diversity schemes can enhance reception significantly under certain circumstances. However, they increase the complexity of the transmitter and the receiver. Also, for some environmental conditions, diversity transmission can reduce the quality of the received signal.